Internal combustion engines, such as those used in automobiles and trucks, are fueled by an air/fuel mixture which is combusted in cylinders. Precise control of the air/fuel mixture ratio is important to optimizing the operation of an internal combustion engine in terms of both performance and exhaust gas emissions.
Prior fuel injector controls are designed to provide precise control of the air/fuel mixture in steady state operations, preferably at a ratio of about 14.6:1. Under transient conditions, such as when the vehicle is accelerated or decelerated, the air/fuel ratio can be changed to become lean or fuel rich for a time on the order of one second or more.
It has been found that engine temperature, manifold pressures, fuel vapor pressure and engine air mass flow rates affect the degree to which air/fuel ratios deviate from ideal conditions.
Fuel injectors do not generally inject fuel directly into the combustion chamber, but instead direct fuel sprayed by a nozzle onto walls of intake ports or valve surfaces. Fuel supplied by a spray to a wall of an intake port either vaporizes or coats the wall of the intake port as a liquid which wets the wall or forms a puddle.
Ideally, all of the fuel supplied would be in the form of a vapor. However, either relatively cool temperatures of the intake port wall on initial start-up or rapid increase in fuel supplied prior to increasing engine speed results in the formation of a sizeable puddle of fuel on the intake port wall.
This phenomenon is described in applicant's prior technical paper entitled "Spray/Wall Interactions Simulation", Servati, Hamid B. and Herman, Edward W., SAE Paper No. 890566, which explains injector spray wall interactions for the purpose of optimizing injector location, design and spray patterns for improving engine performance. As explained in that paper, two phenomena are considered in fuel vaporization: (i) conductive fuel vaporization; and (ii) convective fuel vaporization.
Conductive vaporization is a function of fuel volatility wherein fuel contact on warm wall surfaces results in evaporation of lower boiling point hydrocarbons. High end hydrocarbons with low vapor pressure remain on the walls in liquid form.
Convective vaporization results from turbulent, forced convection of fuel into the air stream. Fuel properties, such as viscosity, density, diffusivity and fuel temperature as well as wall surface temperature, air flow, intake manifold pressure, charge temperature, engine speed and the area of the vaporization surface, all affect convective vaporization.
Fuel is transported into the engine cylinder in either gaseous or liquid form, the liquid form being provided by the flow of a fuel puddle on the intake port wall to the intake port.
While these phenomena have been known, dynamic utilization of this information in injector control systems has not heretofore been developed.